Replace SSLContext reference kept in botocore.httpsession

[mckirk]

This should fix #179.

[sethmlarson]

I don't love that we're going to have to do this for many other libraries :/ Boto doesn't support a way to configure SSLContexts?

[mckirk]

I don't love that we're going to have to do this for many other libraries :/ Boto doesn't support a way to configure SSLContexts?

Yeah, it's admittedly not so cool that these hacks are apparently necessary... but botocore even seems to go out of its way to get an 'unpatched' SSLContext: https://github.com/boto/botocore/blob/develop/botocore/httpsession.py#L40

But maybe they'd be open to removing that, the commit that introduced this is seven years old:
boto/botocore@9ce22db